1. Field of the Invention
The present invention relates to an assembled camshaft for engine and a production method thereof, and more particularly to the assembled camshaft including a cam lobe piece and a hollow shaft member and the production method thereof.
2. Description of the Related Art
As an environment surrounding automobile, an improvement in fuel consumption has become a major social concern, and as its countermeasure, lightening of parts has been received keen attention.
As for the lightening of a camshaft for engine, there suggests an assembly system in which a cam lobe piece is mechanically fastened to a hollow shaft member. In the assembled camshaft, a sprocket which is driven to be rotated by a belt or a chain is fastened by a bolt. For this reason, the camshaft requires a structure for receiving a reaction force at the time of fastening the sprocket.
For example, there suggest a structure having a hexagonal nut shaped part which is inserted and fastened in a mouth expanded manner, a structure having a slit (excavation or groove) (see Japanese Patent Application Laid-Open No. 11-270307 (1999)), and a structure having a plane which is cut to be formed.
However, the structure having the hexagonal nut shaped parts causes an increase in cost due to an increase in number of parts and a loss of a lightening effect. Further, since a size of the hexagon is large, there arises a problem that a degree of a design freedom of an engine, particularly of a cylinder head portion, is lowered.
Since the structure having a slit requires a special exclusive working tool, there arises a problem that attachment/detachment of the camshaft is difficult in a general service factory. Namely, since a work using the special working tool is forcibly required in a machine maintenance business, maintainability has a problem.
Further, in the structure having the plane cut to be formed, lowering of mechanical durability is feared. On the contrary, in the case where an entire thickness is previously kept according to a thickness after the cutting, lightening of parts is inhibited.